Polyvalent metals incorporated in enzymes, hormones, and vitamins play an important role in biochemical processes. Because of their ability to change the oxidation state, they serve as electron carriers and participate in the regulation of such important processes as, for example, respiration and photosynthesis. Iron belongs to these metals first of all. Deficiency of iron in a human body retards its growth, makes breathing difficult, causes anemia, and reduces the levels of the production of immune cells. Iron is considered a key metal in energy transformations that occur in green plants and are required for synthesis and other vital processes in cells. Natural water is one of the sources of iron ingress to living organisms from the biosphere.The maximum permissible concentration for iron(III) is 0.3 mg/L in fresh water and 0.05 mg/L in sea water [1]. In actual practice, the concentrations of soluble iron species in natural waters vary from 10 -6 M for river water to 10 -9 M for coastal sea water and to 10 -11 M for ocean water, respectively [2]. Atomic-absorption spectrometry, inductively coupled plasma-mass spectrometry, and stripping voltammetry (SVA) are used for determining trace amounts of iron(III) in natural water. SVA differs from the other methods by its simplicity, compactness, and inexpensive equipment and can be used at the place of sampling. Stationary mercury-drop [2-13] and a mercury-film [14, 15] electrodes are usually used for determining iron(III) by SVA. To lower the detection limit for iron(III) at a mercury electrode to 10 -9 -10 -10 M, organic reagents are used. 1-Nitrozo-2-naphthol [2, 3, 11], catechol [4, 14], 2,3-dihydroxynaphthalene [5, 6], Solochrome Violet [9, 15, 16], Cupferron [10], and 2-(5'-bromo-2'-pyridylazo)-5-diethylaminophenol [12,13] are used most often. However, the extremely high toxicity of metallic mercury makes researchers search for ecologically safe electrodes. A thick-film graphite-containing electrode modified with calomel (TFGME) [17] belongs to such electrodes. In the course of analysis, a very thin dropletlike mercury coating is formed, but, in spite of this, this electrode can be considered safe, because, after analysis, the thin mercury layer can be easily and completely converted back to calomel.This work is dedicated to the development of a procedure for determining trace amounts of iron(III) ions in natural and drinking waters by SVA using a nontoxic thick-film modified graphite electrode. EXPERIMENTALThe reagents used were of high-purity or cp grades. All solutions were prepared with triply distilled water. Solutions of iron(III) of different concentrations (from 10 -2 to 10 -3 M) were prepared by diluting a solution of a certified reference material of Fe(III) (GSO 7254-96) containing 1 mg/mL iron(III) ions with triply distilled water. The supporting electrolytes were 0.01 M ammonia, 0.1 M acetate, and 0.07 M phosphate buffer solutions, a 0.1 M universal buffer mixture, a 0.1 M sodium acetate solution, and a 0.01 M TRIS (hydroxymethylaminomethane) buffer ...
A mercury-free thick-film graphite-containing electrode modified with formazan is proposed for determining manganese(II) by cathodic stripping voltammetry. The detection limit for manganese(II) found with this electrode is 0.04 µ g/L at a preconcentration time of 60 s. The analytical signal from manganese(II) is a linear function of its concentration in the range 0.1 to 30 µ g/L. The results of determining manganese in natural and drinking waters are presented.
Wine is a highly valuable beverage obtained by fermenting natural grape juice. The chemical composition of wine is very complex: besides ethanol, sugars, and organic acids, wine contains tannins, aromatic and coloring substances, and microelements [1]. The information about the quantitative concentration of various components of wine at all stages of wine making allows viniculturists to control the process of obtaining highquality wine that possesses a certain taste, bouquet, color, flavor, and transparency. The stripping voltammetry (SVA) technique is used for determining heavy metals in wines, because it is highly sensitive, selective, rather simple, requires low-cost equipment, and can simultaneously determine several elements and their species [2][3][4][5][6][7][8][9][10][11]. The adsorption of organic substances on the electrode surface, their interaction with metal ions with the formation of electrochemically inert species, and the superposition of the currents of electrochemical transformations of organic substances on the analytical signal of an element under study are serious interferences in SVA. Organic substances adsorbed on the electrode can form a layer capable of affecting the rate of diffusion of analyte ions and changing the kinetics of the electrode process. To eliminate the effect of organic substances on the voltammetric determination of metal ions, different methods of pretreating samples are widely used. Of them, dry mineralization [12,13], wet ashing with strong oxidizing agents (HNO 3 , H 2 O 2 , HClO 4 ) and solubilizers (H 2 SO 4 , HCl, NH 3 ) [7-9], and ultraviolet irradiation in the presence of oxidizing agents or photocatalysts [9][10][11] are the most extensively employed. The disadvantages of the first two methods of wine decomposition are possible losses of a component to be determined upon heating and the contamination of a sample with impurities contained in the reagents introduced. The third method is rather long (1-4 h) and does not always completely decompose the organic matrix, which results in systematic errors of analysis.Simple and rapid electrochemical methods of sample preparation that do not lead to a contamination of samples and a loss of analytes are described in the analysis of natural water, biological fluids, and some foodstuffs. It was proposed that an alternating current (50 Hz) of different asymmetry and density be passed through a test sample in the anodic compartment of a flow membrane electrolyzer [14]. Such a method of sample digestion allowed Cu(II), Pb(II), and Cd(II) to be determined in 30 min. Another method of electrochemical sample preparation allowed organic substances to be removed either by direct anodic oxidation or by indirect oxidation with electrogenerated oxidants [15][16][17]. For such a method of electrochemical mineralization [15], a three-electrode electrolyzer with separated cathodic and anodic compartments was used to prevent the deposition of metal cations on the cathode. A glassy carbon crucible served as the working electrode and elect...
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